Auckland’s listed Chief Post Office (CPO) is to have its foundations replaced while the City Rail Link underground rail line is dug underneath.
Work on the project includes the removal of the 350 tonnes of steel that is providing temporary support for the structure during tunnel construction, and the demolition of 15 concrete piles. While it is carried out, the 14,000-tonne building will be allowed to move by a maximum of 3mm.
The post office will settle back on its original spot, but on foundations that include diaphragm walls sunk 20m below ground, as well as foundation columns and cross beams.
Other buildings, such as Birdcage Tavern near Auckland’s Victoria Park road tunnel, were moved further away while underpinning took place, but this was not possible for the CPO as there was little free space in central Auckland.
Scott Elwarth, City Rail Link’s head of delivery, said: "Underpinning a building the size and weight of the CPO is an extremely challenging task, something only done when other methods are not available and, then, done very slowly.
"The CPO is one of the most historically important buildings in the country, a building with a top heritage rating. All our planning, design and construction of the tunnels has been dominated by the need to protect the CPO from any damage. Add in the tight working conditions for our teams under all that masonry and concrete and the ‘live’ Britomart station on the other side of the wall, then you’re dealing with a challenging engineering operation."
Following the underpinning, restoration work will begin on the building’s interior, due to be completed in late 2020.
Image: Auckland Chief Post Office was built in 1912 (Ingolfson/Wikimedia Commons/Public domain)